146 MOEPHOLOGY AND EVOLUTION
The enamel of the post-canine teeth is not crenated or folded.
DENTITION IN THE ORANG-OUTAN.
The upper central incisors are much wider than the upper lateral incisors, but the crowns are all small as in the Gibbons. There is frequently a marked overbite. The canines form strong tusks capable of piercing the
shells of fruits.
The enamel of the post-canine teeth is wrinkled and crenated, particularly on the lower molars. The wrinkling appears during development, and Gregory (509) regards it as an advanced specialization.
The upper premolar teeth are relatively stouter than in the Gibbons, and their antero-posterior diameter is less than the transverse. The first has a large outer and a small inner cusp, but the second tooth has nearly equal cusps. The first lower premolar is shorter than in the Gibbons, but longer than in the Chimpanzee; and its outer surface is abraded by the upper canine tooth. The first tooth has a large outer and a small inner cusp; whereas the second tooth, 'which approaches a molar tooth in character, has two nearly equal cusps.
The upper molar teeth have quadrilateral crowns and four cusps. The protocones and metacones are connected by oblique ridges; but the hypocones may be reduced, or replaced by small tubercles (Duckworth). The first and second teeth are equal in size and smaller than the third, which exhibits degeneration. The lower molar teeth are long and narrow, and have five cusps.
Supernumerary molar teeth are by no means uncommon in the Orang, as can be seen from a study of